Automatic fuel ignition and heat detection system



P. ROMANELLI Nov. 1, 1966 AUTOMATIC FUEL IGNITION AND HEAT DETECTION SYSTEM Filed Oct. 11, 1965 FIG. 2.

INVENTOR. PA T ROMAA EZ 2 i A77" 'O1?/Vy United States Patent 3,282,324 AUTOMATIC FUEL IGNHTIUN AND HEAT DETECTION SYSTEM Pat Rcmanelli, Bronx, N.Y., assignor to Ram Domestic Products Company, Englewood, N..l., a partnership Filed Oct. 11, 1965, Ser. No. 494,376 Claims. '(Cl. 158-126) The present invention relates to improvements in automatic ignition systems for gas fired devices, and in particular relates to a novel and improved automatic ignition and detection system for gas burners.

The invention herein is intended for use in gas fired appliance installations wherein automatic ignition systems are required for the control of fuel flow and for ignition of the fuel at the proper time. Systems of this type incorporated in gas fired clothes dryers, for example, must be infallible in operation and must incorporate safety features which minimize dangerous conditions in the automatic operation.

In general, the functioning of systems of this type ineludes the operations of energizing an ignition element under the control of a timing mechanism, automatically opening a gas valve to permit gas to flow through the burner when the ignition element has reached an igniting temperature, and thereafter deenergizing the ignition element after the gas has been properly ignited. As a safety feature, means are provided for automatically shutting off the flow of gas in the event that the gas is not ignited after a reasonable lapse of time, or in the event that the gas flame is extinguished accident-ally.

Automatic systems of this type are generally known and in commercial use. In order to regulate the flow of gas, these systems employ heat responsive means which detect the temperature of the ignition element and sense the arrival of this temperature to the degree necessary to ignite gas. At that time, the sensing means actuates the gas valve to permit gas to flow to the heated ignition element. The sensing means also serves the function of detecting the increase in temperature resulting from ignition of the gas and automatically. deenergizing the ignition element when the gas is properly burning. Hitherto such sensing means has been in the nature of a heat responsive element such as a bimetal or expansive member which moves in response to temperature increases and transmits this motion mechanically to switches or other controls. In applicants US. Patent No. 3,183,959, for example, an elongated metal rod is mounted in temperature sensing proximity to the ignition unit and the burner flame, and expands under temperature increases to actuate a lever which in turn operates switches incorporated in electrical circuits for cont-rolling the gas valve and ignition element.

Such mechanical temperature sensing control arrangements hitherto used have the inherent disadvantage of depending upon mechanical movement for their operation, and are thus subject to breakage, wear and improper functioning due to mechanical faults.

It is the object of the present invention to provide an improved automatic ignition and detection system of the type described, which is capable of performing all of the functions of the known commercial systems, but which functions entirely electrically.

Another object of the invention is the provision of an automatic ignition and detection system in which the temperature sensing element is of a solid state nature, in-.

pact assembly with few parts and a simplified electrical circuit, enabling it to be used in installations having a minimum of available space, and affording large economies in manufacture.

In accordance with the invention herein, there is provided in one illustrative embodiment an automatic fuel ignition system for a gas heater having a burner, a solenoid operated gas valve, and a source of power which is activated when gas is to be fed and ignited. The system comprises an ignition element in proximity to the gas burner, the ignition element being made of a substance, such as silicon carbide, which has a negative temperature ooefiicient resulting in the electrical resistance of the element decreasing as the temperature thereof increases. The ignition element is in series in an electrical circuit with the low resistance actuating coil of a solenoid, this circuit also having in series a normally closed first pair of contacts of a switch controlled by an armature of said solenoid. Another armature of the same solenoid controls the opening and closing of a gas valve of said burner. The circuit is so arranged that the ignition element is initially heated when the circuit is energized, but the resistance of the ignition element is sufiiciently high to have no effect upon the gas valve. When the heat of the energized ignition element reaches gas ignition temperature, the resistance thereof has decreased to a point where the actuating coil of the solenoid opens the gas valve, permitting gas to flow through the burner and over the ignition element, so that the gas is ignited.

The burner is arranged so that the flame of the burn-' 'ing gas impinges on the ignition element raising its temperature to a selected level well above gas ignition temperature. When this occurs, the resistance of the ignition element is reduced to a point where the solenoid is sufiiciently energized to attract the armature controlling said switch, which causes the first pair of contacts to open to d'eenergize the solenoid actuating coil and to cause a second pair of contacts to close to ener ize a holding coil for said solenoid. This holding coil is of high resistance, decreasing the energizing current fed to the ignition element.

A further feature of the system resides in a normally closed safety lock-out switch in series with the solenoid actuating coil and having a bimetallic arm intimately associated with a heater coil in series with the ignition element and first pair of switch contacts. The heater coil is energized to heat the bimetallic arm so long as the first pair of contacts are closed, and if the gas does not ignite within a preselected safety period to open the first pair of contacts, the bimetallic arm is heated sufiiciently to move to a position in which it opens the interlock switch and closes the gas valve.

Additional objects and advantages of the invention will become apparent during the course of the following specification when taken in connection with the accompanying drawings, in which:

FIG. 1 is a top plan view of a gas burner installation incorporating the automatic ignition and detection system of the present invention, and

FIG. 2 is a diagrammatic view of the ignition and detection system, showing the electrical circuitry thereof schematically.

Referring in detail to the drawings, and particularly to FIG. 1, there is shown the burner portion of a gas fired appliance such as a clothes dryer, this burner portion being designated generally by the reference numeral 10. The burner is fed by a pipe 12 leading to a source of gas under pressure and communicating with a conventional pressure regulator A- which is standard equipment in such appliances and is employed to reduce the gas line pressure to the proper burner pressure. The gas regulator 14 is connected by a suitable fitting to a magnetic gas control valve 16 mounted in a housing 18. The housing 18 also contains all of the electrical components of the ignition and control system, with the exception of the exposed ignition element, as will be presently described, thus providing a compact, economical arrangement, requiring a minimum of space.

The gas valve 16 extends within the housing 18 and is coupled therein to an outlet pipe 20 which communicates with and feeds the gas burner 22 which terminates in a flared outlet or nozzle portion 24. The outlet pipe 20 is connected to the burner 22 through a conventional air shutter 26 which controls the mixture of air with the gas fed to the burner 22.

Incorporated in the gas supply and burner assembly described above is the ignition and control system designated generally by reference numeral 30 in FIG. 2. This system includes an ignition element 32 coiled upon an electrically insulating tubular support 34 carried by a rigid metal tube or cable 36 which encloses the electrical wiring for energizing the ignition element 32. The tube 36 is supported adjacent its forward free end by a bracket 38 aflixed to the burner 22. As can be seen in FIG. 1, the parts are so constructed and arranged that the ignition element 36 is closely adjacent the outlet end of the burner flared nozzle portion 24 so as to ignite the gas flowing therefrom, so as to be located in intimate heat-sensing relationship to the flame emitted from the burner nozzle.

The rearward end of tube 36 terminates in a plug-in connector 40 which mounts the tube end in the housing 18 and connects the lead wires within the tube to the electrical components and circuitry contained within said housing.

Reference is now made to FIG. 2, which shows the ignition and detection system 3th schematically, and also shows the circuit employed for automatic operation thereof. The magnetic valve 16 is shown as having a valve seat 42 which is normally blocked by the pointed end 44- of a movable valve stem 46. Valve stem 46 is made of magnetically-permeable metal, and is slidably mounted in a bore 48 at one end of the fixed core 50 of a solenoid 52 in such a manner that the stem 46 serves as an armature of the solenoid 52. The valve stem 46 is normally urged downwardly out of bore 48 by a compression spring 54 connected at one end on the end of stem 46 and at the other end on the top wall of bore 48, so that the pointed tip 44 is held seated within the valve seat 42. The solenoid 52 also includes an actuating coil 56 and a holding coil 58, both intimately associated with the coil 50 for successive energization thereof, as will be presently described.

Also arranged to be actuated by solenoid 52 is a singlepole, double-throw switch 60 having a pivoted switch arm 62 carrying at its end a pair of oppositely-facing contacts 64 and 66, arranged to make contact alternately with respective fixed contacts 68 and 70. The switch arm 62 is normally biased by spring 72 to the upward position shown in FIG. 2, in which the contact 64 engages the fixed contact 68. For this purpose, the switch arm 62 may have a lever extension 62a connected at one end to spring 72, the other end of which is anchored to a fixed portion of housing 18, as indicated at 74. On its lower surface the switch arm 62 mounts a block or plate 76 of magneticallypermeable material which is located in proximity to the end of solenoid core 50 so as to be attracted thereby and serve as another solenoid armature, in a manner to be presently described.

The circuit shown in FIG. 2 also includes a safety lockout switch 86 which includes a pair of switch arms 82 and 84 carrying respective facing contacts 36 and '88 at their free ends. The arm 84 is bimetallic, and is so arranged that when heat is applied thereto by a heater coil 9%, forming part of the switch 80, the arm 84 will bend away from the arm 82, or in a direction to open the contacts 86, 88. The latter contacts are normally maintained in the closed position shown in FIG. 2 by a permanent magnet 92 mounted on switch arm 82 and a magnetically-permeable 4t armature 94 mounted on the bimetallic arm 84 close to and in registry with the magnet 92. The switch also incorporates an adjustment screw 96 to compensate for varying ambient temperatures affecting bimetallic arm 84, and to adjust for warp out time of lock-out switch 8t).

It will be seen in FIG. 2 that the circuit shown therein provides means for connecting the ignition element 32 across a pair of terminals 100 and 162 of a power supply source which may be a standard house power line supplying volt alternating current. More specifically, it will be seen that one side of ignition element 32 is connected to terminal ltill by a lead 104 through an on-oif switch 106 which may be automatically operated by a timer mechanism such as is usually provided in automatic clothes drying machines or similar appliances. The opposite side of ignition element 32 is connected by lead 1638, through rectifier 112), to switch 66 and through switch arm 62 and the normally-closed contact pair 64, 68 to lead 112. The heater element $0 is connected in series with lead 112, which is connected by lead 114 to the opposite power source terminal 102, completing a circuit branch in which the ignition element 32 is connected in series with switch 69 and heater coil 90' across power terminals 160, 102.

The actuating coil 55 of solenoid 52 is connected in parallel with said circuit branch, a lead 116 connecting one side of coil 56 to lead 112 and through the latter to power source terminal 100, and a lead 118 connecting the other side of coil 56 to the bimetallic arm 84 of lockout switch 80. This circuit branch is completed by lead 114 which connects the other arm 82 of switch 86 to the power source terminal 162. Rectifier 110 is adapted to supply half-wave rectified DC. current to the coils of solenoid 52.

An alternate circuit branch is provided for the holding coil 58 of solenoid 52, this branch including a lead 120 connecting one end of coil 58 to the fixed contact '70 of switch 60, and a lead 122 connecting the other end of coil 53 to the lead 118. A filter condenser 124, connected by leads 126 and 128 between the leads 16-8 and 118 is provided to smooth out the pulses of the half-wave rectified DC. current.

A novel and important feature of the invention resides in the composition of the ignition element 32 which in itself serves as a heat detector and automatically controls the sequence of operation of the system without the aid of additional mechanical parts. The ignition element 32 is made of silicon carbide which has a negative temperature coeificient such that current flow therethrough is at a maximum when the ignition element has attained maximum temperature. In a commercial embodiment of the system herein, the ignition element 32 was made of such silicon carbon composition manufactured by The Carborundum Company under the trade-' mark Globar. The ignition element was 1 inches in over-all length, and inch. in diameter, this size unit being rated at 2.5 amps at 80 volts. its resistance at room temperature was measured at 130 ohms, decreas ing to approximately 100 ohms at its electrically energized gas ignition temperature of 1600 F., and further decreasing to approximately 85 ohms when heated by the gas flame of an adjacent burner to a temperature of 1800 F.

In operation, when the on-olf switch 106 is closed by.

the timer, thermostat, or similar mechanism to start the operation, the switch 66 is in the position shown in FIG. 2 with its contacts 64 and 68 in engagement, and the circuit branch of ignition element 32 is closed through the closed contacts of lock-out switch 32. The ignition element 32 is, therefore, energized and begins to heat. The element 32 during this initial heating has a relatively high resistance, which is high enough to prevent energization of solenoid starter coil 56 sufficiently to overcome the biasing force of spring 54 on armature or plunger 46. That is to say, the tension of spring 54 is so selected relative to the initial resistance of the energized ignition element, that the spring force maintains the valve When the ignition element 32 reaches an ignition temperature, namely temperature suflicient to ignite gas flowing through the burner, its resistance becomes reduced.

to the point at which it energizes the solenoid actuating coil 56 sufliciently that core 50 magnetically attracts plunger 46 and lifts the latter away from valve seat 42, against tension of spring 54. Gas now begins to flow from feed pipe 12 through outlet pipe 26 and burner 22, escaping through the flared nozzle portion 24. The nozzle portion 24 is so located that some of this gas flows upon the heated ignition element 32 and is ignited, producing the burner flame.

Up to this point, the energization of the actuating c3il 56 of relay 52 and the consequent magnetization of core 50 has not been suflicient to attract the block 76 carried by arm 62 of switch 60 against the tension of spring 72.

When the burner flame is ignited, however, the flame impinges upon the ignition element 32, raising its temperature above that which could be achieved by electrical en ergization alone. This increase in temperature further lowers the electrical resistance of said ignition element 32, allowing more current to flow to solenoid actuator coil 56. Core 56 is thereby magnetized to a point where its force of attraction upon the block 76 carried by switch arm 62 overcomes the biasing force exerted by spring 72 upon arm 62. The block 76 is then drawn down into contact with the end of core 55) causing switch arm 62 to pivot downwardly so as to open contacts 64, 63 and close contacts 66, 76. The circuit branch energizing actuating coil is thus open, and the branch energizing holding coil 52 is thus closed, resulting in energization of holding coil 58 and deenergization of actuating coil 56. Specifically, holding coil 58 is now connected across power source terminals 1% and 102 by leads 114 and 118 and 1122 through closed lock-out switch 80, and by leads 126, M8 and 164- through engaged contacts 66, 70, switch arm 62 and ignition element 32.

The actuating coil 56 of solenoid 56 has a low resistance, whereas the holding coil 58 has a high resistance. Thus, when initially energized the ignition element 32 is in series with the high current, low resistance circuit of actuating coil 56, and when heated by the gas flame, is in series with the low current, high resistance circuit of holding coil 58. In the latter condition, the high resistance of holding coil 58 decreases the current to a value which does not appreciably energize ignition element 36, although the ignition element is maintained at a high temperature by impingement of the flame from burner nozzle 24.

As a safety feature, if the flame emitted by the burner nozzle 24 is accidentally extinguished, or for any reason is materially reduced in quantity or diverted from ignition element 32, the resistance of said ignition element will increase and current to relay holding coil 58 will decrease to a point where spring '72 will return switch arm 62 to its raised position, opening contacts 66, 70 and closing contacts 64, 68, and the ignition cycle is repeated. If the ignition element 32 is broken, the complete system becomes inoperative since all circuit branches are interrupted, and the burner valve 16 closes and remains closed so that no gas can escape from the burner.

The safety lock out switch 80 provides a means whereby the gas flow will be interrupted if the gas emitted by the burner nozzle 24 is not ignited by the ignition element 32 within a reasonable time. Since the heater coil 90 of switch 80 is in series with the ignition element 32, this coil 90 is energized simultaneously with the ignition element 32 from the time the circuit is initially activated by closing of on-off switch 106. As-the heater coil 96 becomes hot, it heats the bimetallic switch arm 84, causing it to tend to bend away from switch arm 82, but the magnet 92 and its armature 94 maintain the switch contacts 86, 88 in closed condition. If the gas valve 16 is now opened and the escaping gas ignited so as to increase the temperature of ignition element 32, the contacts 64, 68 are opened, deenergizing the heater coil 90 and allowing bimetallic arm 84 to cool and the switch contacts 86, 88 to remain closed during the entire burner operation. If, however, the gas is not ignited and the ignition element 32 not increased in temperature thereby, the energized heater coil 96 will continue to heat bimetallic arm 84 until it is warped sufliciently to overcome the force of magnet 92. The bimetallic arm 84 will then snap away from the arm 82, opening contacts 86, 88 and breaking the circuit through lead 118 to actuating coil 56. Said actuating coil is then deenergized, releasing valve stem 46 to close gas valve 16 and cut off the supply of gas. The switch will remain open under the heat of coil as long as switch contacts 64, 68 remain closed and the circuit therethrough remains energized. When the circuit is deenergized, the bimetallic arm 84 cools and returns to normal position, where it is magnetically attracted by magnet 92, and the lockout switch contacts 86 and 88 are reclosed so that the ignition circuit may again be operated.

While a preferred embodiment of the invention has been shown and described herein, it will be obvious that numerous omissions, changes and additions may be made in such embodiment without departing from the spirit and scope of the invention.

What is claimed is:

1. An automatic fuel ignition and heat detection system for gas fired devices having a source of electrical power, a burner provided with an outlet, and a normally closed fuel valve for controlling the flow of gas into said burner, said system comprising variable resistance means in proximity to said burner outlet for igniting gas flowing therethrough and to receive the heat of the flame emitted by said burner, electromechanical means responsive to a first predetermined amplitude of current for opening said fuel valve, electrical circuit means connecting said variable resistance means in series with said electromechanical means across said power source for energization and heating of said variable resistance means when said circuit means is completed, said electromechanical means being responsive to a second, higher amplitude of current for maintaining said fuel valve in open condition and reducing the electrical energization of said variable resistance means, said variable resistance means being responsive to increases in temperature for initially maintaining the current in said circuit below said predetermined amplitude and for increasing the current in said circuit to said first predetermined amplitude when the variable resistance means is energized to a temperature sufficient to ignite the burner gas, said variable resistance means being also responsive to the heat of the ignited burner gas to increase the current in said circuit to said second amplitude of current.

2. An automatic fuel ignition and heat detection system for gas fired devices having a source of electrical power, a burner provided with an outlet, and a normally closed fuel valve for controlling the flow of gas into said burner, said system comprising an ignition element in proximity to said burner outlet for igniting gas flowing therethrough and to receive the heat of the flame emitted by said burner, electrically operable actuating means responsive to a first predetermined value of current for opening said fuel valve, electrical circuit means connecting said actuating means with said ignition element and said power source for energization of said ignition element when said circuit means is completed, said actuating means being responsive to a second predetermined value of current for maintaining said fuel valve in open condition and reducing the electrical energization of said ignition element said ignition element being made of a material having a negative temperature coeflicient with an initially high electrical resistance which decreases in response to the increase in temperature of said element, said ignition element having sufficient resistance during initial energization and heating to maintain said actuating means inoperative and said gas valve closed, the resistance of the ignition element when heated to a gas-igniting temperature being such that said actuating means is sufliciently energized to open said gas valve, whereby gas flows through said burner to said ignition element only after the latter has reached a gas-igniting temperature, the resistance af said ignition element decreasing further in response to the heat of the ignited gas flowing from the burner such that the current through the actuating means reaches said second predetermined value.

3. An automatic fuel ignition and heat detection system for gas fired devices having a source of electrical power, a burner provided with an outlet, and a normally closed electromagnetic fuel valve for controlling the flow of gas into said burner, said system comprising an ignition element in proximity to said burner outlet for igniting gas flowing therethrough and to receive the heat of the flame emitted by said burner, a solenoid for opening said fuel valve and including an actuating coil, electrical circuit means connecting said actuating coil in series with said ignition element across said power source for energization of said ignition element when said circuit means is completed, said ignition element being made of a material having a negative temperature coefficient with an initially high electrical resistance which decreases in response to the increase in temperature of said element, said ignition element having suflicient resistance during initial energization and heating to maintain said solenoid actuating coil sufficiently deenergized that said gas valve remains closed, the resistance of the ignition element when heated to a gas-igniting temperature being such that said actuating coil is sufliciently energized to open said gas valve, whereby gas flows through said burner to said ignition element only after the latter has reached a gasignition temperature, and holding circuit means for energizing said solenoid to maintain said fuel valve in open condition, said holding circuit means being operable by said actuating coil when the current therethrongh reaches a preselected value through a further decrease in the resistance of said ignition element in response to the heat of ignited gas flowing through said burner.

4. An automatic fuel ignition and heat detection system for gas fired devices having a source of electrical power, a burner provided with an outlet, and a normally closedfuel valve for controlling the flow of gas into said burner, said system comprising variable resistance means in proximity to said burner outlet for igniting gas flowing therethrough and to receive the heat of the flame emitted by said burner, solenoid means for controlling said fuel valve and including an actuating winding for opening said gas valve and a holding winding for maintaining said gas valve in open condition, an actuating circuit connecting said actuating winding and variable resistance means in series with said power source, a holding circuit connecting said holding winding and variable resistance means in serieswith said power source, said actuating winding being responsive to a first predetermined amplitude of current to open said gas valve and being also responsive to a second predetermined amplitude of current higher than said first amplitude for opening said actuating circuit and closing said holding circuit, said variable resistance means being responsive to increases in temperature for initially limiting the current in said actuating circuit below said first predetermined amplitude and for increasing the current in said actuating circuit to said first predetermined amplitude when the variable resistance means is electrically energized to a temperature sufficient to ignite said burner gas, said variable resistance means increasing the current in said circuit to said second predetermined amplitude in response to the heat received from the flame emitted by said burner.

5. An automatic fuel ignition and heat detection system for gas fired devices having a source of electrical power, a burner provided with an outlet, and a normally closed fuel valve for controlling the flow of gas into said burner, said system comprising an ignition element in proximity to said burner outlet for igniting gas flowing therethrough and to receive the heat of the flame emitted by said burner, solenoid means for controlling said fuel valve and including an actuating winding for opening said gas valve and a holding winding for maintaining said gas valve in open condition, an actuating circuit connecting said actuating winding and ignition coil in series with said power source for energization of said ignition element when said actuating circuit is completed, a holding circuit connecting said holding winding and ignition element in series with said power source, said actuating winding being responsive to a first predetermined amplitude of current to open said gas valve and being also responsive to a second predetermined amplitude of current higher than said first amplitude for opening said actuating circuit and closing said holding circuit, said ignition element eing made of a material having a negative temperature coefficient with an initially high electrical resistance which decreases in response to the increase in tempera ture of said element, said ignition element having suflicient resistance during initial energization and heating to limit the current in said actuating circuit below said first predetermined amplitude whereby said gas valve remains closed, the resistance of the ignition element when heated to a gas-igniting temperature being such that the current in said actuating circuit is increased to said first predetermined amplitude whereby said salenoid' means opens said gas valve, said ignition element increasing the current in said actuating circuit to said second predetermined amplitude in response to an increase in heat thereof when the flame of ignited gas flowing from said burner impinges said ignition element.

6. A system according to claim 5 which also includes switch means in series with said power source and actuating and holding circuits, and time delay means for actuating said switch means to open said circuits after said actuating circuit has been energized for a selected time interval, said time delay means being in series with said ignition element in said actuating circuit 7. An automatic fuel ignition and heat detection system for gas fired devices having a source of electrical power, a burner provided with an outlet, and a normally closed electromagnetic fuel valve for controlling the flow of gas into said burner, said system comprising an ignition element in proximity to said burner outlet for igniting gas flowing there through and to receive the heat of the flame emitted by said burner, solenoid means for opening said fuel valve and including an actuating coil and a holding coil, first electrical circuit means connecting said actuating coil in series with said ignition element across said power source for ener-gization and heating of said ignition element when said circuit means is completed, second circuit means connecting said holding coil in series with said ignition element across said power source, switch means having a first operative position completing said first circuit means and a second operative position opening said first circuit means and completing said second circuit means, biasing means normally urging said switch means to said first operative position, said solenoid means being operatively associated with said switch means to actuate and bring the same to said second operative position at a selected amplitude of energization, said ignition element having a high ne ative temperature coefficient with an initially high electrical resistance which decreases in response to the increase in temperature of said element, and having sufficient resistance during initial energization and heating to maintain the actuating coil of said solenoid means inoperative to open said gas valve, the resistance of said ignition element when heated to a gas igniting temperature decreasing to such an extent that said actuating coil is sufiiciently energized to open said gase valve, the resistance of the ignition element when heated by the flame of the ignited burner further decreasing sutficiently to cause said solenoid means to bring said switch means to its secondope-rative position, whereby the ignition element is in series with said holding coil across said power terminals.

8. A system according to claim 7 in which said holding coil has a sufficiently high resistance to limit current flow through said ignition element to a value below that required to electrically energize said ignition element to a fuel-igniting temperature, when said holding coil is in series with said ignition element in said second circuit means.

9. A system according to claim 7 which also includes lock-out means for deener-gizing said ignition element after a selected time period of operation, said lock-out means including a heating element in said first circuit means, said heating element being energized to start the operation of said lock-out means While said ignition element is energized by said first circuit means, and being deenergized to halt operation of said lock-out means he fore said selected time period has elapsed when the flame of said gas burner raises the temperature of said ignition element to a level at which said first circuit means is opened and said second circuit means is completed.

10. A system according to claim 9 in which said lockout means includes a lock-out switch in series with said power source and first and second circuit means, said switch including a bimetallic element in intimate association with said heating element and movable to a position to open said lock-out switch when said heater element reaches a pre-selected temperature.

References Cited by the Examiner UNITED STATES PATENTS 2,095,253 10/1937 Heyroth 1751 15 2,596,729 5/1952 See 158125 2,772,727 12/1956 Schell l58--28 3,122,316 2/1964 Leigh 1 236l 3,171,019 2/1965 Riddel 2l9519 FREDERICK KETTERER, Primary Examiner. 

1. AN AUTOMATIC FUEL IGNITION AND HEAT DETECTION SYSTEM FOR GAS FIRED DEVICES HAVING A SOURCE OF ELECTRICAL POWER, A BURNER PROVIDED WITH AN OUTLET, AND A NORMALLY CLOSED FUEL VALVE FOR CONTROLLING THE FLOW OF GAS INTO SAID BURNER, SAID SYSTEM COMPRISING VARIABLE RESISTANCE MEANS IN PROXIMITY TO SAID BURNER OUTLET FOR IGNITING GAS FLOWING THERETHROUGH AND TO RECEIVE THE HEAT OF THE FLAME EMITTED BY SAID BURNER, ELECTROMECHANICAL MEANS RESPONSIVE TO A FIRST PREDETERMINED AMPLITUDE OF CURRENT FOR OPENING SAID FUEL VALVE, ELECTRICAL CIRCUIAT MEANS CONNECTING SAID VARIABLE RESISTANCE MEANS IN SERIES WITH SAID ELECTROMECHANICAL MEANS ACROSS SAID POWER SOURCE FOR ENERGIZATIONAND HEATING OF SAID VARIABLE RESISTANCE MEANS WHEN SAID CIRCUIT MEANS IS COMPLETED, SAID ELECTROMECHANICAL MEANS BEING RESPONSIVE TO A SECOND, HIGHER AMPLITUDE OF CURRENT FOR MAINTAINING SAID FUEL VALVE IN OPEN CONDITION AND REDUCING THE ELECTRICAL ENERGIZATION OF SAID VARIABLE RESISTANCE MEANS, SAID VARIABLE RESISTANCE MEANS BEING RESPONSIVE TO INCREASES IN TEMPERATURE FOR INITIALLY MAINTAINING THE CURRENT IN SAID CIRCUIT BELOW SAID PREDETERMINED AMPLITUDE AND FOR INCREASING THE CURRENT IN SAID CIRCUIT TO SAID FIRST PREDETERMINED AMPLITUDE WHEN THE VARIABLE RESISTANCE MEANS IS ENERGIZED TO A TEMPERTURE SUFFICIENT TO IGNITE THE BURNER GAS, SAID VARIABLE RESISTANCE MEANS BEING ALSO RESPONSIVE TO THE HEAT OF THE IGNITED BURNER GAS TO INCREASE THE CURRENT IN SAID CIRCUIT TO SAID SECOND AMPLITUDE OF CURRENT. 